Table of Contents
Advertisement
Section 14 A/D Converter
14.7.6
Notes on Noise Countermeasures
A protection circuit connected to prevent damage due to an abnormal voltage such as an excessive
surge at the analog input pins (AN0 to AN7) should be connected between AVcc and AVss as
shown in figure 14.9. Also, the bypass capacitors connected to AVcc and the filter capacitor
connected to the AN0 to AN7 pins must be connected to AVss.
If a filter capacitor is connected, the input currents at the AN0 to AN7 pins are averaged, and so an
error may arise. Also, when A/D conversion is performed frequently, as in scan mode, if the
current charged and discharged by the capacitance of the sample-and-hold circuit in the A/D
converter exceeds the current input via the input impedance (R
input pin voltage. Careful consideration is therefore required when deciding the circuit constants.
1
*
*
Notes:
Values are reference values.
1.
2. R
Figure 14.9 Example of Analog Input Protection Circuit
Table 14.6 Analog Pin Specifications
Item
Analog input capacitance
Permissible signal source impedance
Rev.2.00 Jun. 28, 2007 Page 542 of 666
REJ09B0311-0200
100 Ω
2
R
*
in
1
0.1 µF
10 µF
0.01 µF
: Input impedance
in
), an error will arise in the analog
in
AV
CC
Vref
AN0 to AN7
AV
SS
Min
Max
20
10
Unit
pF
kΩ
Advertisement
Table of Contents
